Metaphor: Imagine being an explorer. You are sent on a mission to find Machu Picchu in the Peru mountains.
You now have quite a few options. You could set out on an excursion with the locals who have a general idea where this ancient masonry could be found. It would cost quite some time, but you’ll not only find Machu Picchu, but also learn so much about the culture, way of living, the lay of the land, the fauna and flora, language, hardships of the tribes,…
You could also hire a helicopter and scan a wide area for any signs of ancient civilization. This could be done in a day. You might also notice the famous Nazca patterns carved in the rocks over miles and miles. On foot, these might not be apparent.
There are plenty more options to go about exploring. Doing any of these may find you different kinds of experiences. Doing them all would give you deep knowledge of this part of the world, but you probably don’t have the time, money or flow to do every possible one.
What it tries to explain: There are tons of test strategies you could envision. Choosing is very dependent on context. How much time do you have? Is it important that you learn about the project? What kind and how in depth do you need to track your testing? Who are you working with? What state is the project in?
All these questions and many more will decide what your approach might be. It requires an intelligent and skillful tester to quickly and smartly decide how to go about testing in order to be productive. Keep in mind that the key to staying productive and profitable for your project is revising your test strategy.
Lesson: While Focus and Defocus are usually heuristics used in actually testing certain parts of the product. They apply very much on your testing strategy as well.